Due to the high level of crystallinity of PPS, monofilaments thereof tend to be brittle and are difficult to work with. In particular, the knot strength and loop strength of PPS monofilament are low and result in problems during the processing of the monofilaments, especially when the monofilament is woven into fabrics. When the monofilament is removed from the quill during weaving, twists and loops form which, when tightened, kink and result in filament breaks.
Mixtures of PPS with various thermoplastic materials have been prepared heretofore, in an effort to reduce the brittleness. In general, the mixtures are not directly extrudable and have not provided the improvement desired.
In U.S. Pat. No. 4,421,588, PPS is blended with polyetheretherketone using diphenylsulphone as a mutual solvent. The resulting mixture, used for bearing material, has high fatigue strength and improved thermal stability but can be formed only by molding.
In U.S. Pat. No. 4,455,410, PPS is mixed with a polyetherimide for the purpose of obtaining a material with good flexural strength and better mechanical properties than PPS alone. The PPS used in the example was Ryton P-4, a powder grade resin, available from Phillips Chemical Co. and which is suitable for molding rather than extruding. The final products described in the patent were produced by extruding a mixture of the components and then molding the mixtures, i.e., a two step process.
In U.S. Pat. No. 4,493,917, PPS (Ryton P-4, molding grade material) is mixed with fluoropolymers in order to improve the properties of the fluoropolymer which in turn is reflected in a modification of the mechanical properties of the components of electrochemical reactors that are made from fluoropolymers, viz., to reduce the high temperature creep and reduce the high thermal coefficient of expansion of the fluoropolymers. The fluoropolymers specified were fully fluorinated homopolymers or perfluoroalkoxy resins. The process of preparing the components required two steps: preparing the blend by extrusion and then producing the final object by molding.
Thus, it will be seen that the present invention has addressed and solved the problem of polyphenylene sulfide monofilament brittleness. Also the extrudability of this monofilament has been improved by the process of the invention. Neither brittleness nor extrudability has been satisfactorily addressed by the art discussed herein.